The goal of this research is to elucidate the molecular basis of S100B protein's involvement in the neuroinflammatory responses of activated glia (astrocytes and microglia). S100B is a glial-derived cytokine that is significantly elevated in the brains of Alzheimer's disease (AD) patients. S100B induces pro- inflammatory cytokines (e.g., IL-1beta and TNFalpha) and oxidative stress related enzymes (e.g. iNOS) in activated glia, and enhances the ability of other stimuli, such as beta-amyloid, to activate glia. These neuroinflammatory responses, in turn, can lead to neuronal dysfunction and further glial activation. Thus, S100B contributes to a vicious cycle of glial activation/ neuroinflammation/neuronal dysfunction that provides the potential for self-propagation of neurodegenerative events and chronic glial activation seen in AD. However, very little is known about the molecular mechanisms by which S100B induces iNOS and pro-inflammatory cytokines, how modulation of these specific molecular pathways in activated glia affects neuronal viability, or how modulation of S100B itself influences glial and neuronal responses. The hypothesis is that responses of glial cells to S100B contribute to and environment that enhances the progression of neuropathology, and that knowledge of the molecular basis of S100B action on glia will provide the potential for blocking specific glial activation pathways that have neurotoxic consequences. Specific aim 1 will address the mechanisms by which S100B activates glia. Aim 1A will examine if S100B stimulates iNOS through a cytokine-dependent, NFkappaB regulated pathway. Aim 1B will determine if p38 and ERK MAP kinases are important for S100B-induced IL-1beta production in activated microglia. Aim 1C will elucidate the potential role of RAGE, a new receptor that can interact with S100B, in mediating the S100B-induced neuroinflammatory responses. Aim 2 will determine the contribution of specific signal transduction pathways leading to iNOS induction on neuronal dysfunction, by utilizing a defined co-culture system of primary astrocytes and neurons where NO- dependent neuronal death occurs. Pathways will be modulated by selective pharmacological agents or molecular constructs, and effects on neuronal viability determined. Astrocytes from genetically engineered mice with overexpression or knockout of specific components of glial signaling pathways will also be used to ascertain how an in vivo alteration in a specific pathway affects neuronal function. Aim 3 will use a discovery approach employing cell-based screens of chemical libraries and recursive synthetic chemistry refinement to discover ligands that modulate S100B production in activated astrocytes. These studies will provide new insight into glial-neuronal interactions and the knowledge base necessary for pursuit of novel strategies to block glial activation and its neurotoxic consequences.